Coal: An Old Source Facing New Challenges Daniel Cohan Rice University October 4, 2014.

Coal: An Old Source Facing New Challenges

Daniel Cohan

Rice University

October 4, 2014

Outline

• Overview of coal and its use• Emissions from coal• Controlling emissions from coal• Other impacts of coal• Costs of coal

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Overview of Coal and its Use

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How Coal Forms

• Plants die in swamp forests and are buried by sediment as peat

• Heat and pressure expel water and gases

• Coal becomes more carbon and energy rich over millions of years

Graphic from Univ of Kentucky

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6

Western coals becoming increasingly prevalent

• Thick seams in West for large-scale mining

• Appalachian coals heavily utilized before, most accessible reserves already tapped

• Western coals have lower sulfur content, lower price– Transportation costs,

bottlenecks are issueUS EIA, AEO 2012

Powder River Basin Coal supplies many TX power plants

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http://www.wildearthguardians.org/images/content/pagebuilder/Powder_River_Basin_distribution_legend-2.jpg

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U.S. uses 1,045,878,000 tons of coal for electric generation each year• 3.5 tons/person/year (~50 times

our weight)

100 tons1 ton

360 tons12 tons

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U.S. Coal Use Trends

• Historically, large use by industry, homes, transportation

• Now power plants predominate

US EIA, AEO 2006

Coal supplies 34% of electricity for the Texas ERCOT grid

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Natural gas45%

Coal34%

Nuclear12%

Wind9%

Other0%

Electricity Generation (MWh) in ERCOT, 2012

Coal is big share of US electricity capacity, but most growth is natural gas & renewables

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Most U.S. coal-fired electricity is from decades-old power plants

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Cohan and Douglass, 2011

Emissions from Coal

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IPCC

Projected climate change depends on CO2 emissions

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IPCC, WGI SPM, 2013

Electricity Generation: Biggest source of greenhouse gases in U.S.

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Highest CO2 emissions from coal(This is life cycle CO2equivalent basis, so

includes CH4 leaks, etc)

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Greenhouse gas impact per kWh:Coal >> Natural gas >> Solar, biomass, wind, nuclear

Weisser, “A guide to life-cycle greenhouse gas emissions from electric supply technologies.” Energy, 2007

Old coal plants emit far more NOx than other options in Texas

18-

0.5

1.0

1.5

2.0

2.5

2003 2004 2005 2006 2007 2008 2009 2010 2011 2012

NO

x E

mis

sion

Rat

e (l

b/M

Wh

)

TXU legacy coal

Other old coal

New coal

10 cleanest old coal

Natural gas

Cohan, 2013

Emissions from Texas power plants

NOx contributes to excess ozone in Texas cities (standard is 75 ppb)

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0

20

40

60

80

100

120

8-h

r O

zon

e D

esig

n V

alu

e (p

pb

)

Houston-Galveston-Brazoria (88)

Dallas-Fort Worth (87)

Beaumont-Port Arthur (80)

San Antonio (80)

Tyler-Longview-Marshall (79)

Waco (75)

Austin-Round Rock (74)

Corpus Christi-Victoria (72)

El Paso (72)

Cohan, 2013

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Ground-level Ozone Impacts

• Health effects– Strong oxidant, irritates lungs– Linked to asthma and other

respiratory illnesses– Recently linked to mortality

• Damage to vegetation & crops• Greenhouse gas• Non-attainment of EPA standards

Old coal plants emit far more SO2 than other options in Texas

21-

2.0

4.0

6.0

8.0

10.0

12.0

14.0

2003 2004 2005 2006 2007 2008 2009 2010 2011 2012

SO2

Em

issi

on R

ate

(lb/M

Wh)

TXU legacy coal

Other old coal

New coal

10 cleanest old coal

Natural gas

Cohan, 2013

Emissions from Texas power plants

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SO2 contributes to fine particulate matter

• Particulate matter: airborne particles composed of a variety of chemical compounds

• Particulate matter is likely the leading cause of illness and mortality from air pollution

Controlling emissions from coal-fired electricity

Timeline of US cap-and-trade policies for air pollutants

http://www.epa.gov/airmarkets/progress/ARPCAIR10_01.html

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U.S. Power Plant Emissions Trends

NOx Emissions SO2 Emissions

http://www.epa.gov/airmarkt/progress/datatrends/index.html

US EPA Policies for CO2 from Power Plants

• Historically, CO2 was not regulated

• 2007: Supreme Court in Massachusetts v. EPA ruled Clean Air Act can cover CO2

• 2013: Proposed New Source Performance Standards of 1000-1100 lb CO2/MWh

– Attained by new natural gas plants– Would require partial capture of CO2 from coal

• 2014: Proposed Clean Power Plan, with CO2 targets for each state– For Texas: 39% reduction by 2030 26

Clean Power Plan CO2 Reduction Targets

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US Power Plant CO2 Trends

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http://www.epa.gov/airmarkt/progress/datatrends/index.html

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Power Plant NOx Control:Selective Catalytic Reduction (SCR)

• Ammonia is injected after boiler to convert NOx to N2 and water– Requires catalyst– Specific temperature

range

• ~85% NOx reduction

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www.de-nox.com

Flue Gas Desulfurization (“Wet Scrubber”) for SO2

US DOE National Energy Technology Laboratory

Rainfall Acidity, 1994

Rainfall Acidity, 2009(Note the reductions in acidity in regions where coal is heavily used for electricity; results from SO2 & NOx controls under Acid Rain Program)

Post-combustion carbon capture

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FIGURE 12.1 Flowsheet of the monoethanolamine (MEA) process for CO2 capture.

Fay & Golomb textbook

• Reaction of liquid solvent MEA with CO2 • C2H4OHNH2 (“MEA”) + H2O + CO2 ↔ C2H4OHNH3

+ + HCO3-

• Need 1 mole MEA per mole CO2 captured• Huge material flows: 400 kg/s MEA for 500MW plant

Forward Reaction @ 40-65°C (flue gas must be cooled)

Reverse Reaction @ 100-120°C (needs steam; hurts efficiency)

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CO2 Transport

• Pipelines– Some CO2 pipelines already exist for

enhanced oilfield recovery– Similar impacts as other hydrocarbon pipelines

• Ships– CO2 could be liquefied for ship transport

• Road or rail– Probably not cost-effective

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Methods for storing CO2 in deep underground geological formations

SRCCS Figure TS-7

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Global distribution of large stationary sources of CO2

Prospective areas in sedimentary basins where suitable saline formations, oil or gas fields, or coal beds may be found.

SRCCS Figure TS-2b

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Geological Storage Capacity

• For comparison, global anthropogenic emissions are about 28 GtCO2/year

IPCC, 2005

Cost of CCS vs. other CO2 control options

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Coal Impacts beyond Air and Climate

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Mountaintop Removal Mining• In much of Appalachia, coal seams may

be hundreds of feet beneath surface• 500 feet or more of a mountain summit

may be removed to access coal

Coal Ash Pond Spill, Kingston (TN) Power Plant, December 2008

Associated Press41

Ash from Coal Power Plants

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Coal Ash• Ash from coal combustion: 10% of original

volume of coal (U.S. EPA)– Fly ash (74%): Mixed with exhaust gas;

captured by various technologies– Bottom ash (20%): Large, settles to bottom– Boiler slag (6%): Ash that melts by heat

• 1,300 coal ash dumps in U.S.– Mercury, lead, arsenic, and selenium in ash– Lack of federal regulation– $5-11 billion/year estimated clean-up costs

N.Y. Times, “Hundreds of Coal Ash Dumps Lack Regulation,” 1/6/200943

Solid Wastes from Coal Power Plants

• Coal combustion generates ~129 million tons/year of wastes in US; ~35% reused

US EPA Coal Combustion Products Partnership

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Cost of Coal Electricity

New coal costs more than gas, wind, or geothermal; with carbon capture, it costs more than solar

Alternatives to coal in Texas

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Cost1

Cost with incentives2

Cost with incentives + $25/ton CO2 3

SO2 4

(lb)

NOx 5

(lb) CO2 6

(lb) Hg 7

(10-5 lb) Water use 8

(gal)

Legacy coal 2011 $39.63 $39.63 $66.34 9.18 1.48 2,137 8.9 300 Coal with UBS retrofits 9

$42.89 $42.89 $70.02 4.36 1.23 2,170 0.9 309

Coal with SCRs 10 $45.29 $45.29 $72.42 4.36 0.59 2,170 0.9 309 Natural gas $65.90 $65.90 $79.51 0.01 0.36 1,089 0.0 270 Geothermal $76.10-

$88.20 $65.10- $77.20

$65.65- $77.75

0.17 0.00 44 0.0 5

Coastal wind $51.00-$83.40

$40.00- $72.40

$40.00- $72.40

0.00 0.00 0 0.0 1

Solar $140.30 $77.90-$101.18

$77.90- $101.18

0.00 0.00 0 0.0 26

Energy efficiency $35.00 $35.00 $35.00 0.00 0.00 0 0.0 0

Cohan, 2013

Costs per MWh generated

Externality costs of coal(National Research Council, 2009)

• 3.2 cents/kWh due to health and other impacts of air pollution– 1.7 cents/kWh by 2030 as emissions are cut– Natural gas impacts are ~0.2 cents/kWh– Other studies estimate much higher impacts from coal

• Wide uncertainty on climate impacts (up to 10 cents/kWh)

• Additional impacts from coal mines and transport

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Projections of coal use depend on climate policy

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GHG15 scenario: US sets CO2 emission price, rising to $44/ton by 2035

US EIA Annual Energy Outlook 2012

Summary of challenges to coal• Old coal plants provide affordable

electricity, but:– Need to control NOx, SO2, and mercury

– Retrofit carbon capture is very expensive– EPA Clean Power Plan will require CO2 cuts

• New coal plants aren’t cost competitive with natural gas or some renewables– Need carbon capture to meet EPA’s proposed

New Source Performance Standards• Impacts to air, climate, land, and water

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